1. Field of the Invention
The present invention relates to a rewritable optical disc, and a recording method and a reproduction method for the optical disc. The present invention in particular relates to an optical disc recording apparatus and an optical disc recording method which each record video objects (compressed audio and video data) so that the seamless reproduction of the video objects is possible even if a pause operation was designated by a user during recording, and an optical disc apparatus for the optical disc recording apparatus and the optical disc recording method.
2. Background Art
In recent years, optical discs with a capacity of several gigabytes, such as DVD-RAMs (digital video disc-random access memories), have appeared in the field of rewritable optical discs that had formerly been limited to a capacity of 650 MB.
It is expected that such optical discs will become the principal media for recording AV (audio-visual) data as well as computer data. That is, it is believed that optical discs and recording and reproduction apparatuses for the optical discs (hereinafter abbreviated to the xe2x80x9coptical disc apparatusesxe2x80x9d) will replace magnetic tapes and VCRs (videocassette recorders) that have conventionally been the major AV data recording media and AV data recording apparatuses.
The operation of an optical disc apparatus used instead of a stationary VCR is described below. The optical disc apparatus receives television signals of a broadcast, converts the signals into a video object, and records the video object onto an optical disc. More specifically, the optical disc apparatus generates compressed video data (a video elementary stream) and compressed audio data (an audio elementary stream) from the television signals, divides the compressed video data into video packs of a fixed length, and divides the compressed audio data into audio packs of a fixed length. Then the optical disc apparatus interleaves the video packs and audio packs and records the interleaved packs onto optical discs as a video object. Here, the video elementary stream and the audio elementary stream are generated according to an MPEG standard (ISO/IEC13818).
The optical disc apparatus usually generates one video object in each recording operation if a pause operation (the temporary halt of recording) is not designated during the recording operation. That is, if no pause operation is designated during recording, the optical disc apparatus generates and records one video object for the period between the time when a user designates the start of recording and the time when the user designates the end of recording.
If a pause operation is designated during recording, a problem arises in the optical disc apparatus. That is, it becomes difficult for the optical disc apparatus to seamlessly reproduce video objects generated before and after a pause operation.
If one video object is generated by each successive recording operation, the optical disc apparatus completes the generation and recording of a current video object on receiving a pause designation and starts to generate and record a new video object on receiving a pause release designation. That is, one video object is generated and recorded for each of the period between a designation of recording start and a pause designation, the period between a pause release designation and the next pause designation, and the period between a pause release designation and a designation of recording end.
If a video object recorded until a pause designation and a video object recorded after a pause release designation are sequentially reproduced, the optical disc apparatus cannot guarantee the seamless reproduction of these video objects and the following problems may occur.
To prevent overflows and underflows of video elementary streams in the video input buffer of a reproduction apparatus, the optical disc apparatus assumes the video input buffer and carries out a simulation to determine the size of data accumulated in the video input buffer during the encoding of video data. Similarly, during the encoding of audio data, the optical disc apparatus assumes an audio input buffer and carries out a simulation to determine the size of data accumulated in the audio input buffer. Although this guarantees that each video object can be seamlessly reproduced by itself, an overflow and underflow may occur in the reproduction apparatus at the boundary between a video object recorded until a pause designation and that recorded after a pause release designation.
Also, each audio elementary stream includes a plurality of audio frames (each audio frame is of 32 ms, for instance). If separate video objects are generated as a result of a pause operation, noise (electric noise) may occur at the boundary between these video objects because the audio frame at the boundary includes audio data having no correlation.
The first object of the present invention is to provide an optical disc recording apparatus and an optical disc recording method which each records video objects in real time before and after a pause operation so that the seamless reproduction of these video objects is achieved without difficulty, and an optical disc reproduction apparatus for the optical disc recording apparatus and the optical disc recording method.
The second object of the present invention is to provide an optical disc recording apparatus and an optical disc recording method which each record video objects so that it can be judged whether the seamless reproduction of these video objects is possible before the reproduction of the video objects, and an optical disc reproduction apparatus for the optical disc recording apparatus and the optical disc recording method.
The stated objects are achieved by an optical disc recording apparatus including: a receiving unit operable to receive designations from a user, the designations including a recording start designation, a recording end designation, a pause designation, and a pause release designation; an encoding unit operable to generate one video object by compressing audio and video data for a period starting when the receiving unit receives the recording start designation or the pause release designation and ending when the receiving unit receives the pause designation or the recording end designation, where if the receiving unit receives the pause release designation, a video object is generated so that the video object is capable of being seamlessly reproduced with an immediately preceding video object in a reproduction apparatus; a generation unit operable to generate a seamless flag each time a video object is generated, the seamless flag showing whether the video object corresponding to the seamless flag is capable of being seamlessly reproduced with an immediately preceding video object in the reproduction apparatus; and a recording unit operable to record, onto an optical disc, each video object generated by the encoding unit and each seamless flag generated by the generation unit.
Here, if the receiving unit receives the pause designation, the encoding unit completes a generation of a current video object and preserves an internal state of the encoding unit at a point when the generation of the current video object is completed, and if the receiving unit receives the pause release designation, the encoding unit starts a generation of a new video object using the preserved internal state as an initial state.
With this construction, when the user inputs the pause designation and then the pause release designation during recording, a video object generated until the pause designation and a video object generated after the pause release designation are recorded in real time so that the seamless reproduction of these video objects is possible. Also, this construction allows a reproduction apparatus to judge whether the seamless reproduction of video objects is possible by referring to the seamless flag before the reproduction of the video objects.
Here, the generation unit obtains, from the encoding unit, a last system clock reference value of the current video object and a first system clock reference value of the new video object, and the recording unit records the seamless flag, the last system clock reference value, and the first system clock reference value onto the optical disc as video object information.
This construction allows the reproduction apparatus to smoothly perform special reproduction, such as reverse quick reproduction, by referring to the system clock reference values in the video object information before the reproduction of video objects.
Here, the encoding unit replaces one of a last section of audio data immediately before the pause designation and a start section of audio data immediately after the pause release designation with silent data, each of the last section and the start section being shorter than one audio frame.
With this construction, the encoding unit replaces the last section or the first section with silent data and then generate compressed audio data. This avoids a situation where data having no correlation successively exists in an audio frame divided by a pause operation. As a result, it is ensured that no noise will occur during reproduction.
The stated objects are also achieved by a reproduction apparatus for an optical disc that records a plurality of video objects and a plurality of pieces of video object information, each video object including compressed video data and compressed audio data, and each piece of video object information corresponding to one video object and including a seamless flag that shows whether the corresponding video object is capable of being seamlessly reproduced with an immediately preceding video object, the reproduction apparatus including: a reading unit operable to read, from the optical disc, a piece of video object information and a video object corresponding to the piece of video object information; a decoding unit operable to generate audio and video data by decoding the video object read by the reading unit; and a control unit operable to control seamless reproduction by the decoding unit according to a seamless flag included in the piece of video object information read by the reading unit.
With this construction, the reproduction apparatus can judge whether the seamless reproduction of a video object is possible by referring to the seamless flag before the reproduction of the video object.
Here, the decoding unit includes: a separating unit operable to separate the video object read by the reading unit into compressed video data and compressed audio data; a video buffer operable to temporarily hold the compressed video data; an audio buffer operable to temporarily hold the compressed audio data; a first decoder operable to decode the compressed video data in the video buffer; and a second decoder operable to decode the compressed audio data in the audio buffer, where if a seamless flag corresponding to a next video object, which should be reproduced next to a current video object, shows that seamless reproduction of the next video object is possible, the control unit controls the decoding unit so that the next video object read by the reading unit is supplied to the first and second decoding units without initializing the video buffer and the audio buffer at a point when the current video object is switched to the next video object.
With this construction, if judging that seamless reproduction is possible, the reproduction apparatus reproduces a video object without initialing video and audio buffers at a point when an immediately preceding video object is switched to the video object. As a result, the reproduction apparatus can seamlessly reproduce video objects without difficulty.
Here, each piece of video object information includes, in addition to a seamless flag, a first system clock reference value of a video object corresponding to the seamless flag and a last system clock reference value of a video object immediately preceding the corresponding video object, and if the seamless flag corresponding to the next video object shows that seamless reproduction of the next video object is possible, the control unit controls the first decoding unit and the second decoding unit to change an internal system time clock according to a first system clock reference value and a last system clock reference value included in a piece of video object information corresponding to the next video object.
With this construction, the reproduction apparatus can smoothly perform special reproduction, such as reverse quick reproduction, of video objects by referring to the system clock reference values in the video object information before the reproduction of the video objects.